Transforming growth factor beta-s (TGFbeta) are a family of multi- functional cytokines produced by platelets, monocytes, and lymphocytes. In many cell types, TGFbeta inhibits proliferation and expression of specific genes by other cytokines. For example, TGFbeta inhibits the stimulation of c-jun by TGFalpha in primary cultures of adult rat hepatocytes. Also, TGFbeta inhibits the stimulation of Type I collagenase by epidermal growth factor (EGF) in primary cultures of human fibroblasts. The mechanisms by which TGFbeta exerts these inhibitory effects are unknown, but appear to be modulated in part by regulation of AP-1 activity. Therefore, this research proposes to study the regulation of AP-1 activity by TGFbeta and its effects on downstream gene regulation. Experiments using primary cultures of hepatocytes and fibroblasts will determine the effects of the interactions of TGFbeta with other agonists on the expression of endogenous genes. Subsequent experiments in collaboration with M. Karin and J. Wang will use reporter genes to identify the TGFbeta responsive elements within the regulated genes, such as collagenase, c-jun and JunB. Finally, the role of TGFbeta in the phosphorylation of c-jun as a post-translational mechanism for regulation will be investigated in collaboration with M. Karin. This proposed research will elucidate the role of the AP-1 nuclear proto- oncogenes in the signal transduction of TGFbeta. This proposal will investigate the following specific aims: 1. To determine the mechanism by which TGFbeta inhibits the induction of c-jun transcription in primary cultures of adult rat hepatocytes. 2. To determine the mechanism by which TGFbeta inhibits the induction of collagenase and c-jun transcription in primary cultures of human fibroblasts. 3. To determine the effect of TGFbeta on protein kinase and phosphatase activity that recognize c-Jun as a substrate. 4. To determine if the cell-specific differences in TGFbeta's inhibiting effects are secondary to differences in expression of TGFbeta receptors.